In orthogonal frequency-division multiplexing (OFDM) networks, a preamble is used for synchronization and channel estimation. In oversampled OFDM networks, the preamble used for time synchronization does not have an ideal autocorrelation function. The ideal function is the Dirac delta function, which represents an infinitely sharp peak bounding unit area. This is due to a guard band, which degrades the accuracy of symbol timing.
Oversampled OFDM is typical of most wireless standards that employ OFDM, such as IEEE 802.11, IEEE 802.16 and 3GPP-LTE. Because it is not possible to obtain and ideal preamble sequence in such cases, it is desired to provide an optimal preamble.